1. Field of the Invention
The present invention relates to a contactless linking device for interconnecting sections of a data bus and, more particularly, to sections of a differential or non-differential bifilar EIA standard data bus.
The field of the invention covers bi-directional data transmissions between two devices, and in particular between two devices that are mutualy isolated, or mobile with respect to each other, or that must be easily separable from each other.
Typical applications for the invention include data transfer across a sealed wall between one zone confined within a hostile environment, e.g. premises inside a nuclear or chemical plant, and another zone in a non-hostile environment, or data transfer between physically separated devices that are both inside a hostile environment, for instance between two submerged devices, or again for data transfer across a non-metallic wall, such as a window or skin, without structurally altering the wall.
The invention can also be used in all instances where a contactless link can advantageouly replace a data transmission link by a connector and/or a flexible connection between two separate or relatively movable devices.
This is the case with connectors that are frequently manipulated (e.g. in medical apparatus) or that are submitted to harsh operating conditions (high humidity, corrosive atmospheres, mud, dust, vibrations . . .), as a result of which there occurs a rapid deterioration of the contacts. There is a similar problem with flexible connections between movable devices. In this case the connections restrict, and can even hinder, relative movements between the contacting portions, and are also more easily damaged.
In particular, the invention can be used in robotics for data transfer between the different movable elements of a robot employed in the car industry, or for data transfer between different parts of a vehicle, or between a towing vehicle and its trailer, or again in the field of agricultural machinery, for data transfer between a tractor and a farming tool or a towed machine.
2. BACKGROUND OF THE RELATED ART
There is described in document JP-A-57-132460 a linking device between a first electrical circuit receiving binary data and a second electrical circuit equipped with data processing means. A common isolation transformer is used for transmitting both the data signals and the energy necessary for powering the second circuit. The primary of the transformer receives a signal modulated by the data to be transmitted. The signal drawn from the secondary of the transformer supplies a rectifier circuit that delivers the supply voltage for the second circuit and is applied to a demodulator. The latter extracts the data and a clock for transmission to the processing means.
Such a device provides only an electrical insulation and does not constitute a contactless link, i.e. a physically separated link between the first and circuits.
Moreover, the aforementioned device introduces a phase shift that makes it quite inappropriate for linking two bus sections in a "transparent" manner, i.e. without interfering with the data transmission protocol of the bus.
Document WO-A-8910551 teaches the concept of contactless transmission by means of a lossless oscillator circuit. When the latter is in the vicinity of a receiver comprising an analog resonator, it transmits energy to the receiver and can thus also send data thereto. The coils for the transmitter and receiver circuits can be planar printed circuits. No embodiment concerning the data transmission is given. Similarly, this document makes no mention of bi-directional data transmission between two sections of a data bus.
Document EP-A-0 285 477 describes a data transmission device operating between coupled vehicles, in which each vehicle is equipped with a transmitter-receiver unit in contactless coupling relation with the corresponding unit of the other vehicle, each unit being connected to an RS 485 type bus. The units are arranged such that the transmitter of one unit faces the receiver of the other unit, the transmitters and receivers of both units consisting of ferrite cores.
With such an arrangement, the transmitter of one unit has to be aligned with the corresponding receiver of the other unit in order to ensure proper data transmission. Any relative movement between the vehicles that is not parallel to the axis of the transmitter-receiver pairs causes a mis-alignment in at least one of the pairs.
Accordingly, the device of document EP-A- 0 285 477 not only calls for a very precise positioning between the two units, but also prohibits relative movements of substantial amplitude between them.